1. Field
Embodiments relate to the execution of critical tasks based on the number of available processing entities.
2. Background
A storage system may control access to storage for one or more host computational devices that may be coupled to the storage system over a network. A storage management application that executes in the storage system may manage a plurality of storage devices, such as disk drives, tape drives, flash drives, direct access storage devices (DASD), etc., that are coupled to the storage system. A host may send Input/Output (I/O) commands to the storage system and the storage system may execute the I/O commands to read data from the storage devices or write data to the storage devices.
The storage system may include two or more servers, where each server may be referred to as a node, a storage server, a processor complex, a Central Processor Complex (CPC), or a Central Electronics Complex (CEC). Each server may be included in a cluster. Each server may have a plurality of processor cores (also referred to as cores) and the servers may share the workload of the storage system. In a two server configuration of the storage system, either server can failover to the other if there is a failure or a planned downtime for one of the two servers. For example, a first server may failover to a second server, if there is a failure of the first server.
A computational device, such as a host or a server of a storage system, may include a plurality of processors and form a multiprocessing system. A computational device may have a processor complex that may have a single core or a plurality of cores, where a core may correspond to a central processing unit (CPU). For example, a dual-core processor complex has two central processing units, so that the dual-core processor complex may appear to the operating system as two CPUs.
A process (or task) is an instance of a computer program that is being executed. Depending on the operating system, a process may be made up of multiple threads of execution that execute instructions concurrently. Multiple threads may exist within the same process and share resources such as memory. A thread is what the CPU actually runs, whereas a process has the allocated memory for instructions and data. A process may need one or more threads because that is what is actually run by the CPU. Multiple threads corresponding to a process implies that the process gets more time slices on the same CPU or gets to run on more CPUs concurrently. A process needs at least one thread that the CPU executes. In a multi-core processor complex, a different process may use a different core at the same time to speed up the system.
U.S. Pat. No. 8,276,142 describes a method that includes scheduling a thread to run on a core of a multi-core processor. U.S. Pat. No. 8,250,347 describes asymmetric hardware support for a special class of threads. US Patent Publication 2005/0015768 describes a method for scheduling tasks. U.S. Pat. No. 6,212,544 describes a method for performing computer processing operations in a data processing system having a multithreaded processor and thread switch logic. U.S. Pat. No. 6,085,215 describes a method using a combination of processing threads, polling, and a use of interrupts to allocate the use of processing resources fairly among competing functions.